A lot of people in Minnesota and the Dakotas (where they also say this frequently) are of German or Norwegian background. My theory is that it might have come from one of those languages. Perhaps in the German or Norwegian languages there is comparable saying, and "you betcha" is how people have translated it into English.

-1. No, there are not. Norwegian has similar constructions to “you can bet [something] on that”, but there is no reason whatsoever to assume that a shortened version, “you betcha”, is derived from the Norwegian, rather than from the English phrase. The standard German phrase used to indicate the same kind of certainty is, as far as I know, “you can drink poison on that”.
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Janus Bahs JacquetJul 21 '13 at 12:47